Acoustic transducers of the type herein contemplated are well known in the art. An exemplary device of this type is disclosed in U.S. Pat. No. 4,823,110. As stated in the patent, a particularly acute problem in producing devices of this type is the manner in which the diaphragm is mounted within the device. In general it can be stated that the functional characteristics provided by the diaphragm in the automotive environment are such that it becomes highly desirable to mount the diaphragm in a manner which can be repeated on a mass production basis sufficient to maintain uniformity in operation without significant variation.
The mounting of the diaphragm is critical in this regard in two functional aspects requiring repeatability without significant variation. The first aspect is that the mounting must serve to accurately position the diaphragm with respect to the pole piece. The second aspect is that the mounting must provide a difficult to consistently achieve acoustical seal for the interior chamber which enables dynamic acoustical sealing to occur while permitting static pressure leakage to occur. The manner of securing the diaphragm to the fixed structure may detrimentally effect these two functional aspects. The interrelationship between the various aspects of the diaphragm mounting materially contribute to the difficulty of the problem presented. The chamber which the diaphragm must acoustically seal contains the pole piece spacing. Consequently, the spacing cannot be conveniently determined after the diaphragm is mounted in acoustically sealed relation. Moreover, the physical contact which the diaphragm is subjected to in accomplishing its mount can effect both the pole piece spacing and the acoustic seal of the chamber as well as the vibrational characteristics of the diaphragm itself.
The mounting arrangement of the '110 patent is to utilize a rigid retaining number having spaced lugs which contact the diaphragm at spaced positions along its marginal periphery. This mode of mounting is described in the patent as replacing prior art modes wherein spaced spot weldings are used to secure the diaphragm to its fixed support or a ring of foam rubber is used to resiliently retain the marginal periphery of the diaphragm on its fixed seat. These structural mountings are difficult to repeat uniformly in such a way as to insure that the functional aspects attributable to the diaphragm mount are achieved.
There is still a need for an automotive chime or transducer which more nearly achieves the desired functional aspects of the diaphragm mount in a more uniformly repeatable manner and in a more cost effective manner.